ISO 1680:2013 pdf free

ISO 1680:2013 pdf free.Acoustics – Test code for the measurement of airborne noise  emitted by rotating electrical machines
When applying ISO 3744 or ISO 3746 which use sound pressure measurements under more or less free-field conditions, a parallelepiped measurement surface shall be used to facilitate the location of the microphone positions.
Supplementing the general rules for rotating electrical machines, the following simplifications may be used.
a) The arrangement of the measurement positions may, especially for large machines, be simplified if, for a specific type of machine, it can be shown, with the help of preliminary investigations on machines of that specific type, that the sound field is adequately uniform and that measurements lead to values of sound power level deviating by no more than 0,5 dB for grade 2 methods and 1 dB (A-weighted) for grade 3 methods from those determined with a complete arrangement of measurement positions.
b) For sources that produce a symmetrical radiation pattern, it may be sufficient to distribute the measurement positions over only a portion of the measurement surface. This is acceptable only if, for a specific type of machine, it can be shown, with the help of preliminary investigations on machines of that specific type, that the measurements lead to values of sound power level deviating by no more than 0,5 dB for grade 2 methods and 1 dB (A-weighted) for grade 3 methods from those determined with a complete arrangement of measurement positions.
c) If required to check the presence of prominent discrete tone(s), the so called “magnetic noise”, being typical of rotating electrical machines, should be taken into consideration with preference. Under no-load operating conditions, this noise component is weak and do not disturb in general, but may increase significantly under loading conditions.
Consequently the following alternative tonality tests are useful for rotating electrical machines:
1) measuring the A-weighted sound power level, LW.A, caused by changing the operating conditions from no-load to rated load to determine the relevant difference OLW,A, in decibels; or
NOTE This test is used by IEC 60034-9[9] where limit values for OLw,A are given.
2) measuring the one-third-octave band pressure spectrum under rated load conditions at the measurement position with the highest value of Lp.A.T and calculation of the difference between each protruding level and its two adjacent band levels.
Differences larger than 6 dB can be characterized as prominent for the frequency range from 500 Hz to 10 000 Hz; or
3) determining the tonality under rated load conditions according to ISO 7779:2010,[3] Annex D.ISO 1680 pdf download.